1. Field of the Invention
The present invention relates to a spread illuminating apparatus, and more particularly to a spread illuminating apparatus used as an illuminating means for a liquid crystal display.
2. Description of the Related Art
A liquid crystal display (hereinafter, referred to as “LCD”) characterized by its low profile, small occupying volume and light weight has been extensively used in a lot of electric products including cellular phones and personal computers, and a demand therefor has been increasing. Since a liquid crystal which is a structural element of the LCD does not emit light by itself, a separate illuminating means besides the LCD is needed when used in dark places where sunlight or room light is not satisfactorily available. In order to satisfy the above requirement, in recent years, a low profile spread illuminating apparatus of side light system (light conductive bar system) has been often used for irradiating the LCD. Thus, in particular, an illuminating means small in size and low in power consumption is required.
FIG. 6 shows a basic structure of a conventional spread illuminating apparatus 1′ of side light system. The spread illuminating apparatus 1′ generally comprises a light conductive plate 2 made of a light-transmissible material, a bar-like lamp 11 consisting of a spot-like light source 12 and a light conductive bar 13 disposed along and close to one end surface 3 of the light conductive plate 2, and a light reflecting member (a reflector) 16 covering three relevant side surfaces of the light conductive bar 13. Light rays emitted from the lamp 11 are allowed to enter the light conductive plate 2 and reflected to irradiate an LCD (not shown) disposed close to a bottom surface of the light conductive plate 2.
The light conductive bar 13, which constitutes the lamp 11, is made of a bar-like light-transmissible material and is disposed along the one end surface 3 of the light conductive plate 2 at a predetermined distance. And the spot-like light source 12, for example, a light emitting diode, is disposed in such a manner as to face one end surface 14 of the light conductive bar 13. An optical path conversion means 15 is formed on a side surface of the light conductive bar 13 opposite to a side surface 18 facing the end surface 3 of the light conductive plate 2. The optical path conversion means 15 comprises, for example, a plurality of grooves arrayed continuously and each having a triangular cross section, and has a function to allow light rays emitted from the spot-like light source 12 to enter the light conductive plate 2 through its end surface 3 in a uniform manner entirely.
A light reflection pattern 7 is formed on a top major surface 6 of the light conductive plate 2 and comprises a plurality of grooves 8 formed parallel to the longitudinal direction of the light conductive bar 13 at predetermined intervals and each having a triangular cross section and a plurality of flat portions 9 each formed between adjacent grooves 8. The grooves 8 are different in depth from one another, specifically, have their depths gradually increasing in proportion to the distance from the end surface 3 of the light conductive plate 2 in order to realize a uniform spread light emission over the light conductive plate 2 independent of the distance from the light conductive bar 13 (lamp 11) for uniform irradiation on the LCD set on the bottom surface of the light conductive plate 2.
The light reflecting member (the reflector) 16 covers the longitudinal side surfaces of the light conductive bar 13 except the side surface 18 facing the light conductive plate 2 so as to allow the light rays emitted from the spot-like light source 12 into the light conductive bar 13 to efficiently enter the light conductive plate 2. The reflector 16 has, on its inner surface, a film on which a metal such as silver is vapor-deposited, a sheet-like material on which a white paint is coated, or a bent metal sheet such as aluminum sheet, stainless steel sheet or the like.
FIG. 7 shows a perspective view of a relevant portion of a conventional spread illuminating apparatus having a housing frame for positioning and fixedly putting together constituent components such as the above-described light conductive plate, light conductive bar and spot-like light source at their respective predetermined locations. FIG. 8 shows a top plan view of the housing frame. Also, FIG. 9A shows a cross-sectional view taken along a line B—B of FIG. 7, and FIG. 9B shows a cross-sectional view taken along a line C—C of FIG. 7. The above-described spread illuminating apparatus was proposed in Japanese Patent Application No. 2001-234887.
A spread illuminating apparatus 1″ shown in FIG. 7 is provided with a housing frame 25 having a mechanism for positioning a spot-like light source 12 (a light emitting diode), a light conductive bar 13 and a light conductive plate 2. The housing frame 25 is made of resin and shaped like a frame. Referring to FIG. 8, the housing frame 25 has a frame-like seat section 27 for positioning the light conductive plate 2 defining an open space 26. Also, the housing frame 25 has, at its one side (an upper side in FIG. 8), recesses 28 and 28 for positioning respective spot-like light sources 12 (not shown in FIG. 8), a flat seat section 29 for positioning the light conductive bar 13. And the housing frame 25 has, at its both sides and close to the recesses 28 and 28, grooves 31 and 31 as guiding sections for an FPC 30 on which the spot-like light sources 12 and 12 are mounted.
As shown in FIGS. 7 and 9B (only one spot-like light source out of the two will be shown for explanation), the FPC 30 is structured so as to extend from the bottom surface of the housing frame 25, through the side surface thereof where it is guided with the groove 31, and through the top surface thereof, and to reach the recess 28 for positioning the spot-like light source 12. The spot-like light source 12 mounted on the FPC 30 is fitted into the recess 28 from the top surface side of the housing frame 25.
As shown in FIGS. 7, 9A and 9B, the spread illuminating apparatus 1″ has a reinforcing frame 32 covering the recess 28 for positioning the spot-like light source 12 and the flat seat section 29 for positioning the light conductive bar 13 from the top surface or from both the top and bottom surfaces. The reinforcing frame 32 has a squared U-shaped cross section and is made of a metal such as a stainless steel. The reinforcing frame 32 comprises a wing portion 32a which is located on the lower surface of the housing frame 25 and which is formed in such a manner as to keep clear of the FPC 30 located on the lower surface of the housing frame 25, and a wing portion 32b which is configured so as to press the FPC 30 as well as the spot-like light source against the recess 28.
The spread illuminating apparatus having the housing frame with the above-described configuration has a certain advantage in that the assembly accuracy can be stabilized or the workability in precisely positioning the components can be enhanced on condition that the light conductive plate 2, the light conductive bar 13 and the spot-like light sources 12 are attached to their respective predetermined positions of the housing frame 25.
However, since the FPC 30 on which the spot-like light sources 12 is mounted extends from the bottom surface of the housing frame 25 through the side surface to the top surface thereof, a surface of the FPC 30 is brought into contact with an edge of the top surface of the housing frame 25. Further, since the FPC 30 together with the spot-like light source is pressed against the recess 28 by the reinforcing frame 32, the FPC 30 is also brought into contact with the top surface of the housing frame 25. Consequently, conductive pattern 41 formed on the surface of the FPC 30 can be broken.
Further, since the spot-like light source 12 mounted on the FPC 30 has to be securely fixed to the recess 28, a temporary fixing tape (for example, a double-face adhesive tape) is stuck on the bottom surface of the spot-like light source 12. The working process is done manually, requiring an additional assembly process, and therefore, an improved workability is required.